Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.71   6.497%   $92.3435   $92.34   $92.35   $92.30  
  Purchase #2 $76.41   13.842%   $86.9867   $86.99   $87.00   $87.00  
  Purchase #3 $151.54   4.278%   $158.0229   $158.02   $158.00   $158.00  
  Purchase #4 $234.25   8.446%   $254.0348   $254.03   $254.05   $254.00  
  Purchase #5 $233.37   6.636%   $248.8564   $248.86   $248.85   $248.90  
  Purchase #6 $98.34   10.742%   $108.9037   $108.90   $108.90   $108.90  
  Purchase #7 $239.64   7.342%   $257.2344   $257.23   $257.25   $257.20  
  7 purchase totals = $1,120.26       $1,206.3824   $1,206.37   $1,206.40   $1,206.30